The invention concerns lumped impedance broad band circulators intended for operating in the 0.02 to 2 GHz band at a mean power of a number of tens of watts.
Power circulators having electrical characteristics which are as far as possible independent of temperature are required in telecommunications.
It is known that a printed circuit suitable for use at high power can be made by depositing conductors on the two faces of an insulating substrate as described, for example, in U.S. Pat. No. 3,522,555 filed on May 6, 1968, and that in addition line sections can be connected in parallel as described in French Pat. No. 2 202 374 filed on Oct. 5, 1973.
It is known to design a circulator having a broad pass band by surrounding the printed circuit and the associated gyromagnetic pellets by a shielding connected to the casing of the circulator by at least one capacitor as described in U.S. Pat No. 3,818,381 filed on May 21, 1973.
It is known--see the article entitled "Broadband circulators for VHF and UHF", published by G. Schiefer, pages 255 to 263, of No. 9, volume 36 of "Philips Technical Review"--to compensate for the variations of the width of the passband of a circulator as a function of the power of the incident wave by incorporating a matching circuit whose inductance has a negative temperature coefficient in each line section connecting a port to the circuit coupled to the gyromagnetic medium. An inductor of this kind is obtained by winding a number of turns on a toroidal ferrite core of the YIG type, disposed in a continuous transverse magnetic field.
The object of the present invention is to provide a circulator having a broad pass band operating in the very high frequency band, or the ultra high frequency band which has electrical characteristics which are independent of temperature between -40.degree. C. and +80.degree. C. without using a matching inductor having a negative temperature coefficient of the type just mentioned.